Group cohesion is the bonding together of members of an organization, team etc in such a way as to sustain their commitment to each other.

Cohesiveness has two dimensions: emotional (or personal) and task-related. The emotional aspect of cohesiveness, which was studied more often, is derived from the connection that members feel to other group members and to their group as a whole. That is, how much do members like to spend time with other group members? Do they look forward to the next group meeting? Task-cohesiveness refers to the degree to which group members share group goals and work together to meet these goals. That is, is there a feeling that the group works smoothly as one unit or do different people pull in different directions?

Factors Influencing Group Cohesiveness
The forces that push group members together can be positive (group-based rewards) or negative (things lost upon leaving the group). The main factors that influence group cohesiveness are: members’ similarity, group size, entry difficulty, group success and external competition and threats. Often, these factors work through enhancing the identification of the individual with the group she/he belongs to as well as their beliefs of how the group can fulfill their personal needs.

Members’ Similarity The more group members are similar to each other on various characteristics the easier it would be to reach cohesiveness. Following Social Identity Theory, we know that people feel closer to those whom they perceive as similar to themselves in terms of external characteristics (age, ethnicity) or internal ones (values, attitudes). In addition, similar background makes it more likely that members share similar views on various issues, including group objectives, how to communicate and the type of desired leadership. In general, higher agreement among members on group rules and norms results in greater trust and less dysfunctional conflict. This, in turn, strengthens both emotional and task cohesiveness.

Group Size Since it is easier for fewer people to agree on goals and to co-ordinate their work smaller groups are more cohesive than larger groups. Task cohesiveness may suffer, though, if the group lacks enough members to perform its tasks well enough.
Entry Difficulty Difficult entry criteria or procedures to a group tend to present it in more exclusive light. The more elite the group is perceived to be, the more prestigious it is to be a member in that group and consequently, the more motivated members are to belong and stay in it. This is why alumni of prestigious universities tend to keep in touch for many years after they graduate.
Group Success Group success, like exclusive entry, increases the value of group membership to its members and influences members to identify more strongly with the team and to want to be actively associated with it.

External Competition and Threats When members perceive active competition with another group, they become more aware of members’ similarity within their group as well as seeing their group as a means to overcome the external threat or competition they are facing. Both these factors increase group cohesiveness; leaders throughout human history have been aware of this and focused the attention of their followers on conflicts with external enemies when internal cohesion was threatened. Similar effects can be brought about by facing an ‘objective’ external threat or challenge (such as natural disaster).